Field of the Invention
The present invention relates to spin drying apparatus for drying plate-like or wafer-like elements, such as semiconductor wafers, during the fabrication of semiconductor components. Wafers used for the manufacture of integrated circuits are subjected to a plurality of fabrication steps including the steps of etching, coating, doping, plating, etc. until the desired multilayered configuration is achieved. After many of the steps, it is desirable to clean the wafer in order to remove contaminants and other particles generated during the previous operation to prepare the wafer for the following operations. The wafers must be cleaned, often on both sides, generally employing a liquid cleaner. After the cleaning step the wafer must be dried in a manner which does not leave contaminants on the surface of the wafer. The cleanliness requirements for semiconductor wafers is such that even films or stains generated by the evaporation of the cleaning fluid can be deleterious.
Heretofore centrifugal drying of wafers has been considered the optimal method of drying semiconductor wafers because the centrifugal force helsp to overcome the surface tension and the resultant clinging of moisture around the edge of a wafer that can result from other forms of drying. Generally, spin drying has been accomplished in the prior art by a vacuum chuck which grips the wafer on the lower face thereof. It has been found that holding the wafer in this manner results in staining of that face of the wafer because the liquid trapped between the chuck and the wafer which either cannot be removed or, during spinning, leaks out from the chuck and is dried as its spreads over the wafer face leaving stains which are unacceptable.
Further, it has been found that the increasing wafer sizes now being utilized to improve semiconductor production efficiency are increasingly difficult to safely hold with vacuum chucks. Any imbalance with larger wafers quickly generate forces which overcome the vacuum force, resulting in the destruction of the wafer as it is flung from the chuck.
One solution for this problem has been to use a spin dryer arranged to grip the edge of the wafer during spinning. A representative type of spin dryer employing edge gripping is disclosed in IBM Technical Disclosure Bulletin, Vol. 18, No. 6 of November 1975 at pages 1979 and 1980. This device includes a plurality of radial arms extending outwardly from a central shaft which is coupled to a drive means for imparting spinning motion to the arms and a wafer held thereby. However, it has been found that with spin dryers of this type, employing radially extending arms to support the wafer at the edge thereof, the arms generates sufficient turbulent air flow that particulate contaminants (solid or liquid) may be picked up by the turbulent air and redeposited upon the cleaned and/or dried surface of the wafer. As the complexity of semiconductor chips increases, along with an ever-decreasing size for the respective components thereon, it becomes more and more important to ensure that the wafers are not only adequately cleaned and dried but are protected against recontamination by contaminants anywhere during the cleaning and drying cycle. It will thus be apparent that the recontamination of already cleaned and dried wafer surfaces by contaminants stirred up by the operation of the spin drying apparatus itself can be extremely unsatisfactory, reducing the yield of the semiconductor devices.